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<h1>Compatibility Notes for rsyslog v3</h1>
<p><small><i>Written by <a href="http://www.gerhards.net/rainer">Rainer Gerhards</a>
(2008-03-28)</i></small></p>
<p>Rsyslog aims to be a drop-in replacement for sysklogd.
However, version 3 has some considerable enhancements, which lead to
some backward compatibility issues both in regard to sysklogd and
rsyslog v1 and v2. Most of these issues are avoided by default by not
specifying the -c option on the rsyslog command line. That will enable
backwards-compatibility mode. However, please note that things may be
suboptimal in backward compatibility mode, so the advise is to work
through this document, update your rsyslog.conf, remove the no longer
supported startup options and then add -c3 as the first option to the
rsyslog command line. That will enable native mode.</p>
<p>Please note that rsyslogd helps you during that process by
logging appropriate messages about compatibility mode and
backwards-compatibility statemtents automatically generated. You may
want your syslogd log for those. They immediately follow rsyslogd's
startup message.</p>
<h2>Inputs</h2>
<p>With v2 and below, inputs were automatically started together
with rsyslog. In v3, inputs are optional! They come in the form of
plug-in modules.
<font color="#ff0000"><b>At least one input module
must be loaded to make rsyslog do any useful work.</b></font>
The config file directives doc briefly lists which config statements
are available by which modules.</p>
<p>It is suggested that input modules be loaded in the top part
of the config file. Here is an example, also highlighting the most
important modules:</p>
<p><b>$ModLoad immark # provides --MARK--
message capability<br>
$ModLoad imudp # provides UDP syslog reception<br>
$ModLoad imtcp # provides TCP syslog reception<br>
</b><b>$ModLoad imgssapi # provides GSSAPI syslog
reception<br>
</b><b>$ModLoad imuxsock # provides support for local
system logging (e.g.
via logger command)<br>
$ModLoad imklog # provides kernel logging support (previously done
by rklogd)</b></p>
<h2>Command Line Options</h2>
<p>A number of command line options have been removed. New config
file directives have been added for them. The -h and -e option have
been removed even in compatibility mode. They are ignored but an
informative message is logged. Please note that -h was never supported
in v2, but was silently ignored. It disappeared some time ago in the
final v1 builds. It can be replaced by applying proper filtering inside
syslog.conf.</p>
<h2>-c option / Compatibility Mode</h2>
<p>The -c option is new and tells rsyslogd about the desired
backward compatibility mode. It must always be the first option on the
command line, as it influences processing of the other options. To use
the rsyslog v3 native
interface, specify -c3. To use compatibility mode&nbsp;,
either do not use -c at all or use -c&lt;vers&gt; where vers is
the
rsyslog version that it shall be compatible to. Use -c0 to be
command-line compatible to sysklogd.</p><p><span style="font-weight: bold;">Please note that rsyslogd issues warning messages if the -c3 command line option is not given.</span>
This is to alert you that your are running in compatibility mode.
Compatibility mode interfers with you rsyslog.conf commands and may
cause some undesired side-effects. It is meant to be used with a plain
old rsyslog.conf - if you use new features, things become messy. So the
best advise is to work through this document, convert your options and
config file and then use rsyslog in native mode. In order to aid you in
this process, rsyslog logs every compatibility-mode config file
directive it has generated. So you can simply copy them from your
logfile and paste them to the config.</p>
<h2>-e Option</h2>
This option is no longer supported, as the "last message repeated n
times" feature is now turned off by default. We changed this default
because this feature is causing a lot of trouble and we need to make it
either go away or change the way it works. For more information, please
see our dedicted <a href="http://www.rsyslog.com/PNphpBB2-viewtopic-p-1130.phtml">forum
thread on "last message repeated n times"</a>. This thread also
contains information on how to configure rsyslogd so that it continues
to support this feature (as long as it is not totally removed).
<h2>-m Option</h2>
<p>The -m command line option is emulated in compatibiltiy mode.
To replace it, use the following config directives (compatibility mode
auto-generates them):</p>
<p><b>$ModLoad immark<br>
$MarkMessageInterval 1800 # 30 minutes</b></p>
<h2>-r Option</h2>
<p>Is no longer available in native mode. However, it
is
understood in compatibility mode (if no -c option is given). Use the <b>$UDPSeverRun
&lt;port&gt;</b> config file directives. You can now also
set the local address the server should listen to via <b>$UDPServerAddress
&lt;ip&gt;</b> config directive.</p>
<p>The following example configures an UDP syslog server at the
local address 192.0.2.1 on port 514:</p>
<p><b>$ModLoad imudp<br>
$UDPServerAddress 192.0.2.1 # this MUST be before the $UDPServerRun
directive!<br>
$UDPServerRun 514</b></p>
<p>"$UDPServerAddress *" means listen on all local interfaces.
This is the default if no directive is specified.</p>
<p>Please note that now multiple listeners are supported. For
example, you can do the following:</p>
<p><b>$ModLoad imudp<br>
$UDPServerAddress 192.0.2.1 # this MUST be before the $UDPServerRun
directive!<br>
$UDPServerRun 514<br>
$UDPServerAddress * # all local interfaces<br>
$UDPServerRun 1514</b></p>
<p>These config file settings run two listeners: one
at 192.0.2.1:514 and one on port 1514, which listens on all local
interfaces.</p>
<h2>Default port for UDP (and TCP) Servers</h2>
<p>Please note that with pre-v3 rsyslogd, a service database
lookup was made when a UDP server was started and no port was
configured. Only if that failed, the IANA default of 514 was used. For
TCP servers, this lookup was never done and 514 always used if no
specific port was configured. For consitency, both TCP and UDP now use
port 514 as default. If a lookup is desired, you need to specify it in
the "Run" directive, e.g. "<i>$UDPServerRun syslog</i>".</p>
<h2>klogd</h2>
<p>klogd has (finally) been replaced by a loadable input module.
To enable klogd functionality, do</p>
<p><b>$ModLoad imklog</b></p>
<p>Note that this can not be handled by the compatibility layer,
as klogd was a separate binary.A limited set of klogd command line
settings is now supported
via rsyslog.conf. That set of configuration directives is to be
expanded.&nbsp;</p>
<h2>Output File Syncing</h2>
Rsyslogd tries to keep as compatible to
stock syslogd as possible. As such, it retained stock syslogd's default
of syncing every file write if not specified otherwise (by placing a
dash in front of the output file name). While this was a useful feature
in past days where hardware was much less reliable and UPS seldom, this
no longer is useful in today's worl. Instead, the syncing is a high
performace hit. With it, rsyslogd writes files around 50 *times* slower
than without it. It also affects overall system performance due to the
high IO activity. In rsyslog v3, syncing has been turned off by
default. This is done via a specific configuration directive
"$ActionFileEnableSync on/off" which is off by default. So even if
rsyslogd finds sync selector lines, it ignores them by default. In
order to enable file syncing, the administrator must specify
"$ActionFileEnableSync on" at the top of rsyslog.conf. This ensures
that syncing only happens in some installations where the administrator
actually wanted that (performance-intense) feature. In the fast
majority of cases (if not all), this dramatically increases rsyslogd
performance without any negative effects.
<h2>Output File Format</h2>
<p>Rsyslog supports high precision RFC 3339 timestamps and puts these into
local log files by default. This is a departure from previous syslogd
behaviour. We decided to sacrify some backward-compatibility in an
effort to provide a better logging solution. Rsyslog has been
supporting the high-precision timestamps for over three years as of
this writing, but nobody used them because they were not default (one
may also assume that most people didn't even know about them). Now, we
are writing the great high-precision time stamps, which greatly aid in
getting the right sequence of logging events. If you do not like that,
you can easily turn them off by placing
</p><p style="font-weight: bold;"><code>$ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat</code>
</p><p>right at the start of your rsyslog.conf. This will use the
previous format. Please note that the name is case-sensitive and must
be specificed exactly as shown above. Please also note that you can of
course use any other format of your liking. To do so, simply specify
the template to use or set a new default template via the
$ActionFileDefaultTemplate directive. Keep in mind, though, that
templates must be defined before they are used.</p><p>Keep in mind that
when receiving messages from remote hosts, the timestamp is just as
precise as the remote host provided it. In most cases, this means you
will only a receive a standard timestamp with second precision. If
rsyslog is running at the remote end, you can configure it to provide
high-precision timestamps (see below).</p><h2>Forwarding Format</h2><p>When
forwarding messages to remote syslog servers, rsyslogd by default uses
the plain old syslog format with second-level resolution inside the
timestamps. We could have made it emit high precision timestamps.
However, that would have broken almost all receivers, including earlier
versions of rsyslog. To avoid this hassle, high-precision timestamps
need to be explicitely enabled. To make this as painless as possible,
rsyslog comes with a canned template that contains everything
necessary. &nbsp;To enable high-precision timestamps, just use:</p><p style="font-weight: bold;"><code>$ActionForwardDefaultTemplate RSYSLOG_ForwardFormat # for plain TCP and UDP</code></p><p style="font-weight: bold;"><code>$ActionGSSForwardDefaultTemplate RSYSLOG_ForwardFormat # for GSS-API</code></p><p>And, of course, you can always set different forwarding formats by just specifying the right template.</p><p>If
you are running in a system with only rsyslog 3.12.5 and above in the
receiver roles, it is suggested to add one (or both) of the above
statements to the top of your rsyslog.conf (but after the $ModLoad's!)
- that will enable you to use the best in timestamp support availble.
Please note that when you use this format with other receivers, they
will probably become pretty confused and not detect the timestamp at
all. In earlier rsyslog versions, for example, that leads to
duplication of timestamp and hostname fields and disables the detection
of the orignal hostname in a relayed/NATed environment. So use the new
format with care. </p><h2>Queue Modes for the Main Message Queue</h2>
<p>Either "FixedArray" or "LinkedList" is recommended. "Direct"
is available, but should not be used except for a very good reason
("Direct" disables queueing and will potentially lead to message loss
on the input side).</p>
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